The present invention relates to an apparatus for measuring the birefringence amount of a liquid crystal panel for use in a liquid crystal display, an optical component such as a glass plate or a lens having an oriented film attached thereto, or an optical disk, and its direction of a lag-phase axis at a speed as high as 0.002 seconds per point and with an accuracy as high as 0.01 nm. More particularly, the present invention relates to an apparatus for observing the distribution of fine molecules oriented by means of rubbing even though an electron microscope is incapable of doing so.
Analyzer-rotating method, phase compensating method, and phase modulating method have been used to measure a birefringence. According to the analyzer-rotating method, an object to be measured is placed behind a polarizer so that the direction of the birefringence forms an angle of about 45.degree. with the polarization direction of the polarizer. An analyzer placed behind the object is rotated. A birefringence amount is calculated based on the maximum and minimum values of the output of a photodetector placed behind the analyzer.
According to the phase compensating method, the polarizer and the analyzer are placed with the axes thereof perpendicular to each other and an object to be measured is placed therebetween with the direction of the birefringence forming about 45.degree.. A Babinet-Soleil compensator is interposed between the object and the analyzer and the Babinet-Soleil compensator is adjusted so that the amount of light which transmits through the object is minimum. The phase compensation amount indicated by the Babinet-Soleil compensator is the birefringence amount to be found.
These conventional methods are incapable of measuring a birefringence amount at a resolution smaller than nm (nanometer). The phase modulating method is capable of carrying out measurements at a higher resolution. According to the phase modulating method, laser beams which have been linearly polarized by about 45.degree. with respect to an x-axis are phase-modulated in the x-axis by a photoelasticity modulator so as to find a birefringence amount based on the phase difference between the beat signal of the beam and the modulated signal thereof which has transmitted through the object.
The details of the phase modulating method is described in optical technology contact Vo. 27, No. 3 (1989) of "Measurement of birefringence by phase modulating method and application thereof" written by Etsuhiro Mochida. This method is capable of measuring a birefringence at a resolution as high as 0.01 nm.
None of the conventional methods are incapable of measuring the direction of the birefringence of the object, namely, the direction of an advance phase axis and that of a lag-phase axis and a birefringence amount. That is, none of the conventional methods are incapable of simultaneously measuring the difference between the phase of transmission light, the electric field of its light wave of which is in the direction of the advance phase axis and the phase of transmission light, the electric field of its light wave of which is in the direction of the lag-phase axis. Therefore, first, the direction of the birefringence is found by measuring the birefringence amount while the object is being rotated about the progress direction of light to be measured and then, the object is placed in the found direction of the birefringence. In this manner, the birefringence amount can be measured. It takes, however, more than a minute to measure the birefringence amount of one point including the period of time required for the rotation of the object.
It is necessary to rotate the object so as to measure the birefringence amount thereof and the direction of the birefringence. Therefore, in order to finely measure the distribution of the birefringence of an entire flat object surface, it is necessary to rotate the object in conformity with the direction of the birefringence at each point to be measured. As a result, the measuring period of time is long. In addition, if a point to be measured is not positioned at the rotational center, the point draws a circle. As a result, measurement errors occur.